Tree response to drought
Rising global temperatures are predicted to increase the frequency and severity of drought in California and many other forested regions of the world, leading to foliage dieback, declining tree growth, increased tree susceptibility to insects and disease, and elevated tree mortality. It is critical to understand how drought impacts tree physiological functioning in order to predict potential forest responses to a changing climate and to develop effective conservation and management strategies in the face of this enormous challenge. I'm currently working to study drought impacts in coast redwood and giant sequoia forests in collaboration with colleagues from the National Park Service, US Geological Survey, Carnegie Institution for Science and others.
Effects of height on tree physiology
What limits tree height? What are the challenges associated with becoming tall? In forest environments, it is advantageous to be tall in order to avoid shading from your neighbors and absorb the most sunlight possible. However, with increasing height comes a cost. As trees get taller, it becomes increasingly difficult to transport water from roots to the treetop against the forces of gravity and friction. While there is more light at the top of a forest, the upper canopy also tends to be warmer and drier than on the ground, increasing atmospheric demand for water. Trees have developed numerous strategies to cope with the challenge of getting tall, including adjustments in leaf and wood morphology, anatomy, and physiology. I'm interested in understanding how increasing tree height constrains the physiology and growth of trees, and how trees adapt to these constraints.
Tree water use dynamics
Terrestrial plants face a fundamental challenge - how to balance the need for carbon with the need to stay hydrated. Plants absorb carbon dioxide from the atmosphere during photosynthesis through tiny pores in their leaves called stomata. During this process, water inside the leaf evaporates through the stomata, creating tension that pulls water from the soil into a plant's roots and up to the leaves. In order to avoid desiccation and hydraulic failure, plants must transport a sufficient supply of water from roots to leaves to replace that which is lost during transpiration. However, if a plant closes its' stomata to reduce water loss, photosynthesis and carbon gain also declines. I'm interested in understanding how large trees have evolved to balance this carbon-for-water trade-off and how this influences tree and forest function.
Canopy microclimate monitoring
Forest canopies are characterized by dramatic vertical gradients in light, temperature, wind, and humidity. These microclimatic gradients have a large effect on the physiology, growth, and survival of trees within a forest. I am currently working to monitor microclimatic conditions at the treetop and near the ground at six long-term research plots in coast redwood and giant sequoia forests established through the Redwoods and Climate Change Initiative. These data are being used to help interpret research at these plots in collaboration with colleagues from Humboldt State University and the Save the Redwoods League. These data are also being used to characterize how environmental conditions vary throughout the range of California's redwood forests, and to track how conditions change over time.
A Note on Tree Climbing
My research has provided me with the opportunity to work in some of the most beautiful forests in the world. I am extremely grateful for this opportunity, and thank the California State Parks, National Park Service, US Forest Service, UC Berkeley Center for Forestry, and UC Natural Reserve system for permission to conduct our research in such amazing places.
Unfortunately, there has been an increase in the frequency of illegal tree climbing in old-growth forests on Park and other public lands in California. I believe that recreational tree climbing is a legitimate activity which can help connect people with nature and increase appreciation for trees and forests. However, old-growth forests are sensitive and fragile ecosystems which are easily impacted by tree climbing, and climbing is not allowed in any California State Park, National Park, or other public land except where authorized by a scientific research or other special use permit.
There are precious few remaining old-growth forests. Please respect the trees, forests, and land managers who are responsible for protecting these extraordinary resources by not climbing illegally. If you are interested, I encourage you to find responsible and legal opportunities to climb or explore redwood and other forest canopies through private companies or guided tours in California and elsewhere. Thanks for your consideration!